Method and apparatus for two-step polishing

ABSTRACT

Methods and apparatus for planarizing a substrate surface having copper containing materials thereon is provided. In one aspect, the invention provides a method for polishing a substrate including polishing the substrate with an abrasive-free polishing pad until it is substantially planarized and then polishing the substrate with a fixed abrasive polishing pad to remove residual materials disposed thereon. Another aspect of the invention provides a computer readable medium bearing instructions for performing the method described herein. In another aspect, the invention provides a system for processing substrates including a first platen, an abrasive-free polishing pad disposed on the first platen, a second platen, a fixed abrasive polishing pad disposed on the second platen, and a computer based controller configured to cause the system to polish the substrate with an abrasive-free polishing pad; and then to polish the substrate with a fixed abrasive polishing pad to remove residual materials disposed thereon.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the fabrication ofsemiconductor devices and to chemical mechanical polishing andplanarization of semiconductor devices.

[0003] 2. Description of the Related Art

[0004] Reliably producing sub-half micron and smaller features is one ofthe key technologies for the next generation of very large scaleintegration (VLSI) and ultra large scale integration (ULSI) ofsemiconductor devices. However, as the fringes of circuit technology arepressed, the shrinking dimensions of interconnects in VLSI and ULSItechnology has placed additional demands on the processing capabilities.The multilevel interconnects that lie at the heart of this technologyrequire precise processing of high aspect ratio features, such as vias,contacts, lines, and other interconnects. Reliable formation of theseinterconnects is important to VLSI and ULSI success and to the continuedeffort to increase circuit density and quality of individual substratesand die.

[0005] In order to further improve the current density of semiconductordevices on integrated circuits, it has become necessary to useconductive materials having low resistivity for conductors and materialshaving low dielectric constant (low k, defined herein as havingdielectric constants, k, less than about 4.0) as insulating layers toreduce the capacitive coupling between adjacent interconnects. Increasedcapacitative coupling between layers can detrimentally affect thefunctioning of semiconductor devices.

[0006] One conductive material gaining acceptance is copper and itsalloys, which have become the materials of choice for sub-quarter-microninterconnect technology because copper has a lower resistivity thanaluminum, (1.7 μΩ-cm compared to 3.1 μΩ-cm for aluminum), a highercurrent and higher carrying capacity. These characteristics areimportant for supporting the higher current densities experienced athigh levels of integration and increased device speed. Further, copperhas a good thermal conductivity and is available in a highly pure state.

[0007] One difficulty in using copper in semiconductor devices is thatcopper is difficult to etch and achieve a precise pattern. Etching withcopper using traditional deposition/etch processes for forminginterconnects has been less than satisfactory. Therefore, new methods ofmanufacturing interconnects having copper containing materials and low kdielectric materials are being developed.

[0008] One method for forming vertical and horizontal interconnects isby a damascene or dual damascene method. In the damascene method, one ormore dielectric materials, such as the low k dielectric materials, aredeposited and pattern etched to form the vertical interconnects, i.e.,vias, and horizontal interconnects, ie., lines. Conductive materials,such as copper containing materials, and other materials, such asbarrier layer materials used to prevent diffusion of copper containingmaterials into the surrounding low k dielectric, are then inlaid intothe etched pattern. Any excess copper containing materials and excessbarrier layer material external to the etched pattern, such as on thefield of the substrate, is then removed.

[0009] As layers of materials are sequentially deposited and removed,the uppermost surface of the substrate may become non-planar across itssurface and require planarization. Planarizing a surface, or “polishing”a surface, is a process where material is removed from the surface ofthe substrate to form a generally even, planar surface. Planarization isuseful in dual damascene processes to remove excess deposited materialand to provide an even surface for subsequent levels of metallizationand processing. Planarization may also be used in removing undesiredsurface topography and surface defects, such as rough surfaces,agglomerated materials, crystal lattice damage, scratches, andcontaminated layers or materials.

[0010] Chemical mechanical planarization, or chemical mechanicalpolishing (CMP), is a common technique used to planarize substrates. Inconventional CMP techniques, a substrate carrier or polishing head ismounted on a carrier assembly and positioned in contact with a polishingpad in a CMP apparatus. The carrier assembly provides a controllablepressure to the substrate urging the substrate against the polishingpad. The pad is moved relative to the substrate by an external drivingforce. Thus, the CMP apparatus effects polishing or rubbing movementbetween the surface of the substrate and the polishing pad whiledispersing a polishing composition to effect both chemical activity andmechanical activity.

[0011] Conventionally, in polishing copper features, such as a dualdamascenes, the copper containing material is polished to the barrierlayer, and then the barrier layer is polished to the underlyingdielectric layer. One challenge which is presented in copper polishingis that the interface between copper and the barrier layer is generallynon-planar. Further, the copper material and the barrier materials areoften removed from the substrate surface at different rates. Thesechallenges in copper removal often results in the retention of coppercontaining material, or residue, on the surface of the substrate. Toensure removal of all the copper material and residue before removingthe barrier material, it is necessary to overpolish the copper and theinterface. Overpolishing of copper and the interface can result informing topographical defects, such as concavities or depressions,referred to as dishing, and can further lead to non-uniform removal ofthe barrier layer disposed thereunder.

[0012] One solution is to remove copper material from the substratesurface in two sequential polishing steps. The first step comprisesusing an abrasive containing slurry on a conventional polishing pad toremove the bulk copper and then removal of the remaining copper by asecond abrasive containing slurry which may also remove a portion of thebarrier layer. However, this two step “slurry-slurry” technique canstill result in an unacceptable amount of dishing.

[0013]FIG. 1 is a schematic view of a substrate illustrating thephenomenon of dishing. Conductive lines 11 and 12 are formed bydepositing conductive materials, such as copper or copper alloy, in afeature definition formed in the dielectric layer 10, typicallycomprised of silicon oxides or other dielectric materials. Afterplanarization, a portion of the conductive material is depressed by anamount D, referred to as the amount of dishing, forming a concave coppersurface. Dishing results in a non-planar surface that impairs theability to print high resolution lines during subsequentphotolithographic steps and detrimentally affects subsequent surfacetopography of the substrate and device formation. Dishing alsodetrimentally affects the performance of devices by lowering theconductance and increasing the resistance of the devices, contrary tothe benefit of using higher conductive materials, such as copper.

[0014] One process that minimizes the effects of dishing is polishingthe substrate surface on a fixed abrasive pad. A fixed abrasivepolishing pad typically contains abrasive particles held in acontainment media which are released during the polishing process.However, fixed abrasive pads require frequent replacing due to wear andprocesses using fixed abrasive pads require longer polishing times whichcan result in lower substrate through-put. One solution to increasesubstrate through-put with fixed abrasive pads is to increase processingpressure between the substrate and the surface of the polishing pad.However, an increased contact pressure during polishing has beenobserved to result in scratching and other defect formation on thesurface of the substrate. Scratching of the substrate surface candetrimentally affect subsequent processing of the substrate anddetrimentally affect device fabrication and performance.

[0015] Another technique to remove copper includes polishing thesubstrate with an abrasive-free polishing composition. Abrasive-freepolishing techniques generally have superior substrate through-putperformance as well as increased wear resistance and reduced substratescratching in comparison to fixed abrasive polishing techniques.However, abrasive-free polishing techniques have exhibited difficulty inremoving all of the copper material from the surface of the substratewhich may remain as undesirable metal residues after the polishingprocess. The presence of residual material can detrimentally effectsubsequent polishing processes, such as barrier layer removal, anddetrimentally affect the polish quality of the substrate surface.

[0016] Therefore, there exists a need for an apparatus, method, andrelated polishing compositions which facilitates the removal of coppercontaining material from the surface of a substrate with minimal orreduced dishing and scratching of the substrate surface.

SUMMARY OF THE INVENTION

[0017] The invention generally provides an apparatus and method forplanarizing a substrate surface having a copper containing materialdisposed thereon. In one aspect, the invention provides a method forpolishing a substrate including polishing the substrate with anabrasive-free polishing pad until it is substantially planarized andthen polishing the substrate with a fixed abrasive polishing pad on asecond polishing platen of the polishing apparatus to remove residualmaterials disposed thereon.

[0018] In another aspect, the invention provides a method forplanarizing a substrate surface, including chemical mechanical polishingthe substrate surface with an abrasive-free first polishing compositionwith an abrasive-free polishing pad on a first polishing platen of apolishing apparatus to substantially remove bulk copper containingmaterials disposed on a substrate surface, and then chemical mechanicalpolishing the substrate surface with a second polishing composition witha fixed abrasive polishing pad on a second polishing platen of thepolishing apparatus to remove residual copper containing materials.

[0019] In another aspect, the invention provides a method for processinga substrate, including providing a substrate having a barrier layer anda copper containing material disposed thereon to a first platencontaining an abrasive-free polishing pad, polishing the substrate at afirst removal rate with an abrasive-free first polishing composition tosubstantially remove the copper containing material disposed thereon,providing the substrate to a second platen containing a fixed abrasivepolishing pad, and polishing the substrate at a second removal rate lessthan the first removal rate with a second polishing composition toremove residual copper containing materials disposed thereon.

[0020] In another aspect, the invention provides a system for processingsubstrates including a first platen adapted for polishing a substratewith an abrasive-free first polishing composition, an abrasive-freepolishing pad disposed on the first platen, a second platen adapted forpolishing the substrate with a second polishing composition, a fixedabrasive polishing pad disposed on the second platen and a computerbased controller configured to cause the system to perform a methodcomprising polishing the substrate with an abrasive-free polishing paduntil it is substantially planarized; and then polishing the substratewith a fixed abrasive polishing pad to remove residual materialsdisposed thereon. The system may further comprise a carousel, at leasttwo substrate head assemblies suspended from the carousel and capable ofholding a substrate thereon, and a positioning member coupled to thecarousel to move the carousel and position the substrate head assembliesover a selected polishing platen.

[0021] Another aspect of the invention provides a computer readablemedium bearing instructions for planarizing a substrate surface, theinstructions arranged, when executed by one or more processors, to causeone or more processors to control a chemical mechanical system toperform polishing the substrate with an abrasive-free polishing paduntil it is substantially planarized and then polishing the substratewith a fixed abrasive polishing pad on a second polishing platen of thepolishing apparatus to remove residual materials disposed thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] So that the manner in which the above recited aspects of thepresent invention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

[0023] It is to be noted, however, that the appended drawings illustrateonly typical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments:

[0024]FIG. 1 is a schematic view of a substrate illustrating thephenomenon of dishing;

[0025]FIG. 2 is a schematic perspective view of a chemical mechanicalpolishing apparatus;

[0026]FIG. 3 is a flow chart illustrating the processing steps accordingto one embodiment of the invention; and

[0027] FIGS. 4-6 are schematic diagrams of a substrate illustrating oneembodiment of a process for planarizing a substrate surface describedherein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] In general, aspects of the invention provide an apparatus, amethod, and compositions for polishing substrates while reducing dishingand minimizing scratching of the substrate surface. The invention willbe described below in reference to the removal of conductive materials,such as copper containing materials, from a substrate surface bychemical mechanical polishing (CMP) techniques. CMP is broadly definedherein as polishing a substrate by chemical activity, mechanicalactivity, or a combination of both chemical and mechanical activity.

[0029]FIG. 2 is a schematic perspective view of a chemical mechanicalpolishing system or apparatus 120 for performing the planarizingprocesses and for use with the CMP compositions described herein. Thepolishing apparatus 120 includes a lower machine base 122 with a tabletop 128 mounted thereon and a removable outer cover (not shown). Thetable top 128 supports a series of polishing stations, including a firstpolishing station 125 a, a second polishing station 125 b, a finalpolishing station 125 c, and a transfer station 127. The transferstation 127 serves multiple functions, including, for example, receivingindividual substrates 110 from a loading apparatus (not shown), washingthe substrates, loading the substrates into carrier heads 180, receivingthe substrates 110 from the carrier heads 180, washing the substrates110 again, and transferring the substrates 110 back to the loadingapparatus.

[0030] A computer based controller 190 is connected to the polishingsystem or apparatus 120 for instructing the system to perform one ormore processing steps on the system, such as polishing a substrate ortransferring a substrate in the polishing apparatus 120. In oneembodiment, the invention may be implemented as a computerprogram-product for use with a computer system or computer basedcontroller 190. The programs defining the functions of the preferredembodiment can be provided to a computer via a variety of signal-bearingmedia and/or computer readable media, which include but are not limitedto, (i) information permanently stored on non-writable storage media(e.g., read-only memory devices within a computer such as read onlyCD-ROM disks readable by a CD-ROM or DVD drive; (ii) alterableinformation stored on a writable storage media (e.g., floppy diskswithin diskette drive or hard-disk drive); or (iii) information conveyedto a computer by communications medium, such as through a computer ortelephone network, including wireless communication. Such signal-bearingmedia, when carrying computer-readable instructions that direct thefunctions of the invention, represent alternative embodiments of thepresent invention. It may also be noted that portions of the productprogram may be developed and implemented independently, but whencombined together are embodiments of the present invention.

[0031] Each polishing station 125 a-125 c includes a rotatable platen130 having a conventional polishing pad 100 or an fixed abrasivepolishing pad 105 disposed thereon. In one aspect of the apparatus for atwo-step copper containing material planarization process using a firstabrasive-free CMP composition on a conventional pad and a secondabrasive-free CMP composition on a fixed abrasive pad, the firstpolishing station 125 a has a conventional polishing pad 100, and thesecond polishing station 125 b has a fixed abrasive pad 105 as shown inFIG. 2. A third polishing station 125 c having a conventional polishingpad 100 may be used for a barrier removal process following the two-stepcopper removal process.

[0032] The fixed-abrasive polishing pad 105 may in one embodimentinclude a multi-layers polishing pad. A lower layer may be attached toplaten 30 by a pressure-sensitive adhesive layer and an upper layer 104typically will be a 5-200 mil thick abrasive composite layer, composedof abrasive grains held or embedded in a binder material. The abrasivegrains may have a particle size between about 0.1 and 1500 microns, andhave a Mohs' hardness of at least 8. Examples of such grains includefused aluminum oxide, ceramic aluminum oxide, green silicon carbide,silicon carbide, chromia, alumina zirconia, diamond, iron oxide, ceria,cubic boron nitride, garnet and combinations thereof. The bindermaterial may be derived from a precursor which includes an organicpolymerizable resin which is cured form the binder material. Examples ofsuch resins include phenolic resins, ureaformaldehyde resins, melamineformaldehyde resins, acrylated urethanes, acrylated epoxies,ethylenically unsaturated compounds, aminoplast derivatives having atleast one pendant acrylate group, isocyanurate derivatives having atleast one pendant acrylate group, vinyl ethers, epoxy resins, andcombinations thereof. The lower layer typically will be a 25-200 milthick backing layer, composed of a material such as a polymeric film,paper, cloth, a metallic film or the like.

[0033] Fixed-abrasive polishing pads are described in detail in thefollowing U.S. patents, all of which are incorporated by reference tothe extent not inconsistent with the invention as claimed and describedherein: U.S. Pat. No. 5,152,917, issued on Oct. 6, 1992, and entitled“Structured Abrasive Article”; U.S. Pat. No. 5,342,419, issued on Aug.30, 1994, and entitled “Abrasive Composites Having A Controlled Rate OfErosion, Articles Incorporating Same, And Methods Of Making And UsingSame”; U.S. Pat. No. 5,368,619, issued on Nov. 29, 1994, and entitled“Reduced Viscosity Slurries, Abrasive Articles Made Therefrom AndMethods Of Making Said Articles”; and U.S. Pat. No. 5,378,251, issued onJan. 3, 1995, and entitled “Abrasive Articles And Method Of Making AndUsing Same”. Fixed-abrasive pads are available from 3M Corporation ofMinneapolis, Minn. and Rodel Inc., of Phoenix, Ariz.

[0034] The platen may support a conventional polishing pad or“abrasive-free” polishing pad 100, i.e., a polishing pad that does nothave embedded abrasive particles, having a smooth polishing surface or aroughened polishing surface. In some embodiments, the abrasive-freepolishing pad may include a single soft layer attached to a platen 30 bya pressure-sensitive adhesive layer. The polishing pad 100 may becomposed of a napped poromeric synthetic material. A suitable softpolishing pad is available from Rodel, Inc., of Newark, Del., under thetrade name Politex. Polishing pad 100 may be embossed or stamped with apattern to improve distribution of slurry across the face of thesubstrate.

[0035] Alternatively, polishing pad 100 may be a standard two-layer padin which the upper layer has a durable roughened surface and is harderthan the lower layer. For example, the upper layer of the two-layer padmay be composed of microporous polyurethane or polyurethane mixed with afiller, whereas the lower layer maybe composed of compressed felt fibersleached with urethane. Both the upper and lower layers may beapproximately fifty mils thick. A two-layer standard pad, with the upperlayer composed of IC-1000 and the lower layer composed of SUBA-4, isavailable from Rodel (IC-1000 and SUBA-4 are product names of Rodel,Inc.).

[0036] A rotatable linear platen may be used for the second polishingstation 125 b. An example of a linear polishing system, and an exampleof a polishing system having a rotatable polishing pad and a rotatablelinear platen, is more fully described in co-pending U.S. patentapplication Ser. No. 09/244,456, filed on Feb. 4, 1999, and incorporatedherein by reference to the extent not inconsistent with the invention.Alternatively, a stationary platen or a rotatable or linear platenhaving a stationary pad may be used for the first, second, or third,polishing stations 125 a, 125 b, and 125 c.

[0037] The invention also contemplates the use of an orbital polishingprocess or orbital polishing platen for the first, second, and/or thirdpolishing stations 125 a, 125 b, 125 c. A substrate and polishing padcan be moved in an orbital relative motion in a linear drive systemwhere the pad is stationary; an example of a apparatus capable ofperforming the orbital relative motion between the polishing pad andsubstrate is the Model 8200, available from Applied Materials Inc., ofSanta Clara, Calif.

[0038] Each platen 130 may be a rotatable aluminum or stainless steelplaten connected to a platen drive motor (not shown). The polishingstations 125 a-125 c may include a pad conditioner apparatus 140. Thepad conditioner apparatus 140 has a rotatable arm 142 holding anindependently rotating conditioner head 144 and an associated washingbasin 146. The pad conditioner apparatus 140 maintains the condition ofthe polishing pad so that it will effectively polish the substrates.Each polishing station may include a conditioning station if the CMPapparatus is used with other pad configurations.

[0039] The polishing stations 125 a-125 c may each have a compositiondelivery/rinse arm 152 that includes two or more supply tubes to provideone or more CMP compositions, cleaning compositions, and/or water to thesurface of the polishing pad. The composition delivery/rinse arm 152delivers the one or more chemical slurries in amounts sufficient tocover and wet the entire polishing pad. Each composition delivery/rinsearm 152 also includes several spray nozzles (not shown) that can providea high-pressure fluid rinse on to the polishing pad at the end of eachpolishing and conditioning cycle. Furthermore, two or more intermediatewashing stations 155 a, 155 b, and 155 c may be positioned betweenadjacent polishing stations 125 a, 125 b, and 125 c to clean thesubstrate as it passes from one station to the next.

[0040] A rotatable multi-head carousel 160 is positioned above the lowermachine base 122. The carousel 160 includes four carrier head systems170 a, 170 b, 170 c, and 170 d. Three of the carrier head systemsreceive or hold the substrates 110 by pressing them against thepolishing pads 100 or 105 disposed on the polishing stations 125 a-125c. One of the carrier head systems 170 a-170 d receives a substrate fromand delivers a substrate 110 to the transfer station 127. The carousel160 is supported by a center post 162 and is rotated about a carouselaxis 164 by a motor assembly (not shown) located within the machine base122. The center post 162 also supports a carousel support plate 166 anda cover 188.

[0041] The four carrier head systems 170 a-170 d are mounted on thecarousel support plate 166 at equal angular intervals about the carouselaxis 164. The center post 162 allows the carousel motor to rotate thecarousel support plate 166 and orbit the carrier head systems 170 a-170d about the carousel axis 164. Each carrier head system 170 a-170 dincludes one carrier head 180. A carrier drive shaft 178 connects acarrier head rotation motor 176 (shown by the removal of one quarter ofthe cover 188) to the carrier head 180 so that the carrier head 180 canindependently rotate about its own axis. There is one carrier driveshaft 178 and motor 176 for each head 180. In addition, each carrierhead 180 independently oscillates laterally in a radial slot 172 formedin the carousel support plate 166.

[0042] The carrier head 180 performs several mechanical functions.Generally, the carrier head 180 holds the substrate 110 against thepolishing pads 100 or 105, evenly distributes a downward pressure acrossthe back surface of the substrate 110, transfers torque from the driveshaft 178 to the substrate 110, and ensures that the substrate 110 doesnot slip out from beneath the carrier head 80 during polishingoperations.

[0043] To facilitate control of the system as described above, thecontroller 190 may include a CPU 192 of FIG. 2, which CPU 192 may be oneof any form of computer processors that can be used in an industrialsetting for controlling various chambers and subprocessors. The memory194 is coupled to the CPU 192. The memory 194, or computer-readablemedium, may be one or more of readily available memory such as randomaccess memory (RAM), read only memory (ROM), floppy disk, hard disk, orany other form of digital storage, local or remote. For storinginformation and instructions to be executed by the CPU 192.

[0044] The support circuits 196 are coupled to the CPU 192 forsupporting the processor in a conventional manner. These circuitsinclude cache, power supplies, clock circuits, input/output circuitryand subsystems, and can include input devices used with the controller190, such as keyboards, trackballs, a mouse, and display devices, suchas computer monitors, printers, and plotters. Such controllers 190 arecommonly known as personal computers; however, the present invention isnot limited to personal computers and can be implemented onworkstations, minicomputers, mainframes, and supercomputers.

[0045] A process, for example a polishing process described below, isgenerally stored in the memory 194, typically as a software routine. Thesoftware routine may also be stored and/or executed by a second CPU (notshown) that is remotely located from the hardware being controlled bythe CPU 192.

[0046] Although the process of the present invention is discussed asbeing implemented as a software routine, some or all of the method stepsthat are disclosed therein may be performed in hardware as well as bythe software controller. As such, the invention may be implemented insoftware as executed upon a computer system, in hardware as anapplication specific integrated circuit or other type of hardwareimplementation, or a combination of software and hardware.

[0047] Chemical Mechanical Polishing Process and Composition

[0048] In one aspect of the invention, a method is provided forplanarizing a substrate surface, comprising polishing the substrate witha first abrasive-free CMP composition to substantially remove bulkcopper containing materials disposed on a substrate surface andpolishing the substrate with a second abrasive-free CMP composition on afixed abrasive polishing pad to remove residual copper containingmaterials.

[0049] Bulk copper containing material is broadly defined herein ascopper containing material deposited on the substrate in an amount morethan sufficient to substantially fill features formed on the substratesurface. Bulk copper containing material can include copper, copperalloys, and/or doped copper. Residual copper containing materials isbroadly defined as any bulk copper containing material remaining afterone or more polishing process steps. Residual copper containing materialcan include copper, copper alloys, and/or doped copper as well asby-products, such as copper oxides, of copper containing materialsremoved from the substrate surface. Residual copper containing materialmay partially or completely cover the surface a substrate, for example,a portion of the underlying barrier layer may be exposed when residualmaterial is retained after a polishing step, or alternatively, nobarrier layer may be exposed after a polishing process has beenperformed.

[0050] The substrate surface generally comprises a dielectric layer withfeature definitions formed therein, a barrier layer deposited on thedielectric layer, and a copper containing material deposited on thebarrier layer. The copper containing material includes copper, copperalloys, or doped copper. As used throughout this disclosure, the phrase“copper containing material” and the symbol Cu are intended to encompasshigh purity elemental copper as well as doped copper and copper-basedalloys, e.g., doped copper and copper-based alloys containing at leastabout 80 wt. % copper. The barrier layer material includes tantalum,tantalum nitride, tantalum silicon nitride. The invention describedherein also contemplates the use of other barrier materials known in theart, such as titanium, titanium nitride, tantalum derivatives, andtitanium silicon nitride, titanium derivatives, and other conventionalbarrier materials.

[0051] The dielectric layer can comprise any of various dielectricmaterials conventionally employed in the manufacture of semiconductordevices. For example, dielectric materials, such as silicon dioxide,phosphorus-doped silicon glass (PSG), boronphosphorus-doped siliconglass (BPSG), and silicon dioxide derived from tetraethyl orthosilicate(TEOS) or silane by plasma enhanced chemical vapor deposition (PECVD)can be employed. The dielectric layer can also comprise low dielectricconstant materials, including fluoro-silicon glass (FSG), polymers, suchas polymides, and carbon-containing silicon dioxide. The openings areformed in interlayer dielectrics by conventional photolithographic andetching techniques.

[0052] In one aspect of the invention, a two step planarizing processfor removing conductive materials and conductive material residues froma substrate surface is provided. In the first step, a firstabrasive-free composition is used with a conventional polishing pad toremove bulk copper containing material. A second abrasive-freecomposition removes residual copper containing material remaining fromthe bulk copper containing material removal process, and which residualcopper containing material removal process advantageously stops on theunderlying barrier layer, thereby planarizing the surface of thesubstrate.

[0053] The bulk copper containing material can be removed using a firstpolishing composition, such as an abrasive-free polishing compositioncapable of removing copper containing material with minimal removal of abarrier material. One example of a suitable first polishing compositionincludes one or more chelating agents, one or more oxidizers, one ormore corrosion inhibitors, one or more pH adjusting agents, a pH ofabout neutral, and deionized water. The first polishing composition mayalso further includes abrasive particles. The first polishingcomposition is well suited for removing copper containing materialsdeposited to fill features formed on a substrate surface describedabove.

[0054] The one or more chelating agents may include compounds having oneor more amine or amide groups, such as ethylenediaminetetraacetic acid,ethylenediamine or methylformamide. The one or more chelating agents mayalso include amino acids or amino acid derivatives, such as glycine, andcarboxylic acids having one or more acids groups, such as citric acid ormaleic acid. The one or more chelating agents can be present in anamount between about 0.02 volume percent (vol %) and about 4.0 vol % ofthe first polishing composition. In one aspect of the invention, thechelating agent comprises between about 0.2 wt. % and about 1.5 wt. % ofthe first polishing composition. The chelating agent chemically reactswith metal ions to form a metal complex which improves removal ofmaterial removed from the substrate surface.

[0055] The one or more oxidizers can be any of various conventionaloxidizers employed in the first polishing compositions and processes,such as hydrogen peroxide, ferric nitrate, or other compounds such asiodates. The oxidizers can be present in an amount between about 0.2 vol% and about 8.0 vol % of the first polishing composition. Aconcentration between about 0.2 wt. % and about 8 wt. % of the oxidizersis used in one embodiment of the first polishing composition.

[0056] Examples of corrosion inhibitors include any various organiccompounds containing an azole group, such as benzotriazole,mercaptobenzotriazole, or 5-methyl-1-benzotriazole. The corrosioninhibitors can be present in an amount between about 0.02 vol % andabout 1.0 vol % of the first polishing composition.

[0057] The pH adjusting agent or agents can be present in an amountsufficient to adjust the pH of the first polishing composition to arange between about 2.5 and about 11 and can comprise any of variousbases, such as potassium hydroxide (KOH) or inorganic and/or organicacids, such as acetic acid, phosphoric acid, or oxalic acid. In oneaspect of the invention, the pH is adjusted to provide a pH andoxidation-reduction potential in the domain of passivation of thepolished material, for example, in the domain of passivation of copper.Additionally, other chelating agents, oxidizers, corrosion inhibitors,and pH adjusting agents are contemplated for use with the invention. Theabove specified components are illustrative and should not be construedas limiting the invention.

[0058] Alternatively, aspects of the invention may include addingabrasive particles to the first polishing composition described herein.Compositions containing abrasives particles may comprise an abrasiveparticle concentration of about 35 wt. % or less of the first polishingcomposition. Alternatively, a concentration between about 2 wt. % orless of abrasive particles is included in first polishing compositionscontaining the one or more surfactants described herein and areconsidered to be abrasive free compositions. Examples of abrasiveparticles include silica alumina, zirconium oxide, titanium oxide,cerium oxide, or any other abrasives known in the art and used inconventional CMP compositions.

[0059] Suitable polishing compositions for removing the bulk coppercontaining material in the first polishing step are more fully describedin co-pending U.S. patent application Ser. No. 09/606,544 filed on Jun.30, 2000, and in co-pending U.S. patent application Ser. No. 09/608,078filed on Jun. 30, 2000, and incorporated herein by reference to theextent not inconsistent with the invention. Suitable polishingcompositions for removing the bulk copper containing material in thefirst polishing step are HC 430-A1-3, HS-C430-A3, HS-C435, HS-A2,commercially available from Hitachi Chemical Co. Ltd., of Japan.

[0060] An example of an abrasive-free first polishing compositiondescribed herein includes between about 0.3 vol % and about 3 vol % ofethylenediamine as a chelating agent, between about 0.5 vol % and about5.0 vol % hydrogen peroxide as the oxidizer, between about 0.02 vol %and about 0.15 vol % benzotriazole as the corrosion inhibitor, andphosphoric acid as the pH adjusting agent to produce a pH level betweenabout 4 and about 8, and distilled water.

[0061] A second polishing composition may be used with a fixed-abrasivepolishing pad in a second planarizing step to remove residual coppercontaining material from the substrate. One example of the secondpolishing composition is the polishing composition including one or morechelating agents, one or more oxidizers, one or more corrosioninhibitors, one or more pH adjusting agents, a pH of about neutral, anddeionized water, described above. Examples of polishing compositionssuitable for use with fixed abrasive copper polishing for removing thecopper containing material in the second polishing step are more fullydescribed in co-pending U.S. patent application Ser. No. 09/543,777filed on May 5, 2000, and in co-pending U.S. patent application Ser. No.09/544,281 filed on Apr. 6, 2000, and incorporated herein by referenceto the extent not inconsistent with the invention.

[0062] One example of the second polishing composition described hereinincludes between about 0.3 vol % and about 3 vol % of ethylenediamine asa chelating agent, between about 0.5 vol % and about 5.0 vol % hydrogenperoxide as the oxidizer, between about 0.02 vol % and about 0.15 vol %benzotriazole as the corrosion inhibitor, and phosphoric acid as the pHadjusting agent to produce a pH level between about 4 and about 8, anddistilled water.

[0063] A suitable commercial second polishing composition for use withthe process described herein is available from 3M of St. Paul, Minn. The3M commercial composition includes between about 2.5 wt. % and about 3wt. % of ammonium hydrogen phosphate, between about 0.5 wt. % and about1 wt. % of iminodiacetic acid, between about 0.04 wt. % and about 0.05wt. % benzotriazole, between about 9 wt. % and about 11 wt. % hydrogenperoxide, and distilled water.

[0064] The second polishing composition used in the second step alsoremoves copper containing material at a removal rate less than theremoval rate of the abrasive-free first polishing composition. The firstpolishing composition removes the copper containing material at a ratebetween about 4000 Å and about 10000 Å per minute, and the secondpolishing composition removes the copper containing material at a rateup to about 4000 Å per minute.

[0065] It is believed that the two-step process reduces dishing of thecopper containing material disposed in the feature reduces scratching ofthe substrate surface during chemical mechanical polishing of thesubstrate surface. Finally, the ability to planarize using anabrasive-free process or a process utilizing a very low concentration ofabrasives results in lower production and operation costs. The processis also compatible with the requirements for manufacturing throughput ona large scale, and is fully compatible with all other aspects ofconventional polishing technology utilized in the manufacture of highintegration density semiconductor devices.

[0066]FIG. 3 is a flow chart illustrating one embodiment of a processfor utilizing the apparatus described herein to remove copper containingmaterials in a two-step planarization process. A substrate is positionedon a first platen containing an abrasive-free polishing pad at step 200,and typically includes positioning a substrate on abrasive-freepolishing pad 100 disposed on platen 130 in polishing station 125 a. Afirst polishing composition is supplied to the polishing pad 100 at step210. Bulk copper containing materials are then removed from the surfaceof the substrate by polishing the substrate at step 220.

[0067] In the polishing process, the carousel 160 positions thesubstrate in contact with the polishing pad 100, and the substrate andthe polishing pad move relative to one another with the compositiondistributed therebetween to effect chemical and mechanical activity onthe substrate, and then the substrate is typically removed from contactwith the polishing pad 100.

[0068] The abrasive-free polishing pad is moved relative to thesubstrate, such as rotated at a rate between about 20 rpm and about 150rpm for a polishing pad disposed on a rotatable platen. In analternative embodiment, the polishing surface is a non-rotary surface,e.g., a linear polishing system, using a sliding or circulatingpolishing belt or similar device.

[0069] The first polishing composition removes substantially all of thebulk copper containing materials formed thereon. The first polishingcomposition may be an abrasive free polishing composition including oneor more chelating agents, one or more surfactants, one or moreoxidizers, one or more corrosion inhibitors, one or more pH adjustingagents, a pH of about neutral, and deionized water, and optionally, a pHadjusting agent and/or abrasive particles, all of which are describedherein.

[0070] The first polishing composition is delivered or supplied to theabrasive-free polishing pad at a flow rate between about 50 ml/min andabout 500 ml/min from a storage medium disposed in or near the CMPapparatus. The substrate and abrasive-free polishing pad are typicallyexposed to the first polishing composition for a period of timesufficient to remove substantially all of the bulk copper containingmaterial disposed thereon.

[0071] For example, the abrasive-free polishing pad may be exposed tothe first polishing composition between about 60 seconds and about 180seconds, but may vary depending upon the material being removed, theconcentration of the components of the first polishing composition, andthe amount or thickness of bulk copper containing material on thesubstrate. A pressure between about 0.5 psi and about 6.0 psi betweenthe substrate and the polishing pad is used to provide mechanicalactivity to the polishing process. The copper containing material isremoved at a rate between about 4000 Å/min and about 10000 Å/min.

[0072] Bulk copper containing material not removed in the above processmay remain as residual copper containing material on the substratesurface. The copper containing material and the residual coppercontaining materials typically comprises copper (Cu), Cu(I), Cu(II),copper oxide (CuO), and combinations thereof.

[0073] The substrate is then positioned on a second platen containing afixed abrasive polishing pad at step 230, and typically includespositioning the substrate on the fixed abrasive polishing pad 105 atpolishing station 125 b. A second polishing composition is supplied tothe polishing pad 105 at step 240. Residual copper containing materialsare then removed from the surface of the substrate by polishing thesubstrate at step 250.

[0074] In the chemical mechanical polishing process, the carousel 160positions the substrate in contact with the polishing pad 105, and thesubstrate and the fixed abrasive polishing pad move relative to oneanother with the composition distributed therebetween to effect chemicaland mechanical activity on the substrate, and then the substrate istypically removed from contact with the polishing pad 100.

[0075] The polishing pad is moved relative to the substrate, such asrotated at a rate between about 20 rpm and about 150 rpm for a polishingpad disposed on a rotatable platen. In an alternative embodiment, thepolishing surface is a non-rotary surface, e.g., a linear polishingsystem, using a sliding or circulating polishing belt or similar device.

[0076] The second CMP composition removes the residual copper containingmaterials described herein that may be formed thereon. The second CMPcomposition includes one or more chelating agents one or more oxidizers,one or more corrosion inhibitors, one or more pH adjusting agents, a pHof about neutral, and deionized water as described herein for the secondpolishing composition.

[0077] The second polishing composition is delivered or supplied to thefixed abrasive polishing pad at a flow rate between about 50 ml/min andabout 500 ml/min from a storage medium disposed in or near the CMPapparatus. The substrate and fixed abrasive polishing pad are typicallyexposed to the second polishing composition for a period of timesufficient to remove the residual copper containing materials disposedthereon and provide for overpolishing of the substrate surface tofurther remove defects formed thereon. For example, the fixed abrasivepolishing pad may be exposed to the second polishing composition betweenabout 60 seconds and about 180 seconds, but may vary depending upon thematerial being removed, the concentration of the components of thesecond polishing composition, and the amount or thickness of coppercontaining materials on the substrate. A pressure between about 0.5 psiand about 6.0 psi between the substrate and the polishing pad is used toprovide mechanical activity to the CMP process. The copper containingmaterial is removed at a rate up to about 4000 Å/min.

[0078] Optionally, a cleaning solution may be applied to the polishingpad during or subsequent each of the polishing process to removeparticulate matter and spent reagents from the polishing process as wellas help minimize metal residue deposition on the polishing pads anddefects formed on a substrate surface. An example of a suitable cleaningsolution is Electra Clean™ commercially available from AppliedMaterials, Inc., of Santa Clara, Calif.

[0079] The substrate may then be positioned on a third platen containinga barrier removal polishing pad at step 260, and typically includespositioning a substrate on abrasive-free polishing pad 100 disposed onplaten 130 in polishing station 125 c. A barrier removal polishingcomposition is then supplied to the polishing pad 100 and barrier layermaterials are then removed from the surface of the substrate by apolishing process on the substrate at step 270. The barrier removalpolishing composition may be an abrasive free composition. Barrierremoval polishing compositions that may be used in the practice of theprocess described herein are commercially available from Hitachi ChemCo. Ltd., of Japan, Cabot Corp. of Aurora, Ill., and Rodel Inc., ofPhoenix, Ariz. One example of commercially available formula suitablefor polishing a barrier layer material is T-605, available from HitachiChemical Co. Ltd., of Japan.

[0080] FIGS. 4-6 are a series of schematic cross-sectional views of asubstrate illustrating sequential phases of a process for forming anin-laid metallization pattern utilizing the two-step planarizationprocess described herein.

[0081] Referring to FIG. 4, the substrate includes a dielectric layer310, such as a silicon oxide or a carbon-doped silicon oxide, formed ona substrate 300. A plurality of openings 311 patterned and etched intothe dielectric in area A forming features for a dense array ofconductive lines with area B being unetched. Typically, the openings 311are spaced apart by a distance C which can be less than about 1 micron,such as about 0.2 micron, or greater than 10 microns, such as 20microns. The openings 311 were formed in the dielectric layer 310 byconventional photolithographic and etching techniques. A barrier layer312 of a conductive material, such as Ta or TaN for a coppermetallization, is disposed conformally in openings 311 and on the uppersurface of the dielectric layer 310. A copper layer 313 is disposed onthe barrier layer at a thickness (D) between about 8,000 Å and about18,000 Å.

[0082] Referring to FIG. 5, the bulk copper material 314 of the copperlayer 313 is removed using a CMP copper polishing process with the firstabrasive-free CMP composition described herein. The first CMPcomposition removes the copper layer 313 to the tantalum barrier layer312. However, residual copper containing material 315 may remain on thesubstrate following the bulk copper containing material removal process.To remove the residual copper containing material, a secondabrasive-free CMP composition is used with a fixed-abrasive polishingpad, which allows for effective removal of the copper layer 313 to thetantalum layer 312, minimizes dishing of the copper later 313, andminimizes formation of a non-planar surface.

[0083] Referring to FIG. 6, the barrier layer is removed by a polishingprocess. The barrier layer removal process typically removes the barrierlayer 312 from the substrate 300 while minimizing dishing of any coppermaterial 313 filling the apertures, and typically stops on thedielectric layer to prevent excessive etching of the dielectricmaterial, thereby completing planarization. Additionally, the dielectriclayer 310 may be polished or buffed during the barrier layer CMP processto remove or reduce scratching or defects formed on the substratesurface. The resulting copper features comprises a dense array (A) ofcopper lines 313 bordered by open field B and the planar surface 314 ofthe copper metallization and substrate 300.

EXAMPLE

[0084] An example of a two-step polishing process according to aspectsof the invention described herein is as follows. A substrate including adielectric layer with feature definitions formed therein, a tantalumbarrier layer conformally deposited on the low k dielectric layer and inthe feature definitions formed therein, and a copper containing layerdeposited on the barrier layer and filling the feature definitionsformed therein is provided to the CMP apparatus disclosed above.

[0085] The substrate is positioned over a first polishing pad of a firstplaten having an abrasive-free polishing pad disposed therein, and anabrasive-free first polishing composition is delivered to the polishingpad. An example of an abrasive-free first polishing compositiondescribed herein includes HS-C430-A3 commercially available from HitachiChemical Co., of Japan. Alternatively, the first polishing compositionincludes about 1.2 vol % ethylenediamine, about 1.5 vol % hydrogenperoxide, about 0.15 vol % benzotriazole as the corrosion inhibitor,sufficient phosphoric acid to produce a pH level of about 7, anddistilled water.

[0086] The substrate is then polished for a requisite amount of time ata rate between about 4000 Å/minute and about 10000 Å/minute tosufficiently remove the bulk of the copper containing material. Apressure between about 0.5 psi and about 6.0 psi between the substrateand the polishing pad is used to provide mechanical activity to the CMPprocess.

[0087] The substrate is then transferred to a second polishing pad on asecond platen having a fixed abrasive polishing pad disposed therein,and a second polishing composition is delivered to the polishing pad. Anexample of a second polishing composition described herein is acommercially available polishing composition available from 3M of St.Paul, Minn., which includes between about 2.5 wt. % and about 3 wt. % ofammonium hydrogen phosphate, between about 0.5 wt. % and about 1 wt. %of iminodiacetic acid, between about 0.04 wt. % and about 0.05 wt. %benzotriazole, between about 9 wt. % and about 11 wt. % hydrogenperoxide, and distilled water. Alternatively, the second polishingcomposition described herein includes between about 0.8 vol %ethylenediamine, about 1.0 vol % of hydrogen peroxide, about 0.2 vol %benzotriazole, sufficient phosphoric acid to produce a pH between ofabout 5.5, and deionized water.

[0088] The substrate is then polished for a requisite amount of time ata rate up to about 4000 Å/minute to sufficiently remove the residue ofthe copper containing material. A pressure between about 0.5 psi andabout 6.0 psi between the substrate and the polishing pad is used toprovide mechanical activity to the CMP process.

[0089] The substrate is then transferred to a third polishing pad on athird platen having an abrasive-free polishing pad disposed therein, anda barrier layer polishing composition is delivered to the polishing padto remove the barrier layer material and planarize the surface of thesubstrate. The barrier removal polishing composition may be an abrasivefree polishing composition.

[0090] While the foregoing is directed to the one or more embodiments ofthe invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow including theirequivalents.

What is claimed is:
 1. A method for polishing a substrate, comprising:polishing the substrate with an abrasive-free polishing pad until it issubstantially planarized; and then polishing the substrate with a fixedabrasive polishing pad to remove residual materials disposed thereon. 2.The method of claim 1, wherein the abrasive-free polishing pad isdisposed on a first platen of a polishing apparatus and the fixedabrasive polishing pad is disposed on a second platen of the polishingapparatus.
 3. The method of claim 2, further comprising supplying afirst polishing composition to the first platen and supplying a secondpolishing composition to the second platen.
 4. The method of claim 1,further comprising polishing the substrate to planarize a barrier layerdisposed on the substrate.
 5. The method of claim 4, wherein polishingthe substrate to planarize a barrier layer comprises supplying with athird polishing composition to a third platen of the polishing apparatusand polishing the substrate with a second abrasive-free polishing paddisposed on the third platen.
 6. A method for planarizing a substratesurface, comprising: chemical mechanical polishing the substrate surfacewith an abrasive-free first polishing composition with an abrasive-freepolishing pad on a first polishing platen of a polishing apparatus tosubstantially remove bulk copper containing materials disposed on asubstrate surface; and then chemical mechanical polishing the substratesurface with a second polishing composition with a fixed abrasivepolishing pad on a second polishing platen of the polishing apparatus toremove residual copper containing materials.
 7. The method of claim 6,wherein the bulk copper containing materials and the residual coppercontaining materials comprise copper, doped copper, or copper alloys. 8.The method of claim 6, further comprising chemical mechanical polishingthe substrate with an abrasive-free third polishing composition on asecond abrasive free polishing pad at a third platen of the polishingapparatus to planarize a barrier layer disposed on the substrate.
 9. Amethod for processing a substrate, comprising: providing a substratehaving a barrier layer and a copper containing material disposed thereonto a first platen containing an abrasive-free polishing pad; polishingthe substrate at a first removal rate with an abrasive-free firstpolishing composition to substantially remove the copper containingmaterial disposed thereon; providing the substrate to a second platencontaining a fixed abrasive polishing pad; and polishing the substrateat a second removal rate less than the first removal rate with a secondpolishing composition to remove residual copper containing materialsdisposed thereon.
 10. The method of claim 9, wherein the first removalrate comprises removing the copper containing material between about4000 Å and about 10000 Å per minute.
 11. The method of claim 9, whereinthe second removal rate comprises removing the copper containingmaterial residue up to about 4000 Å per minute.
 12. The method of claim9, further comprising supplying a first polishing composition to thefirst platen and supplying a second polishing composition to the secondplaten.
 13. The method of claim 9, further comprising providing thesubstrate to a third platen containing a second abrasive-free polishingpad disposed thereon and polishing the substrate to remove the barrierlayer.
 14. A system for processing substrates, comprising: a firstplaten adapted for polishing a substrate with an abrasive-free firstpolishing composition; an abrasive-free polishing pad disposed on thefirst platen; a second platen adapted for polishing the substrate with asecond polishing composition; a fixed abrasive polishing pad disposed onthe second platen; and a computer based controller configured to causethe system to perform a method comprising: polishing the substrate withan abrasive-free polishing pad until it is substantially planarized; andthen polishing the substrate with a fixed abrasive polishing pad toremove residual materials disposed thereon.
 15. The system of claim 14,further comprising a third platen adapted for polishing a barrier layeron the substrate with an abrasive-free third polishing composition, andan abrasive-free polishing pad disposed on third platen.
 16. The systemof claim 15, wherein the first, second, or third platen comprises arotational, stationary or linear polishing platform.
 17. The system ofclaim 14, wherein the computer based controller configured to cause thesystem to perform a method further comprising polishing the barrierlayer on the substrate with an abrasive-free polishing pad until it issubstantially planarized.
 18. The system of claim 14, furthercomprising: a carousel; at least two substrate head assemblies suspendedfrom the carousel and capable of holding a substrate thereon; and apositioning member coupled to the carousel to move the carousel andposition the substrate head assemblies over a selected platen.
 19. Acomputer readable medium bearing instructions for planarizing asubstrate surface, the instructions arranged, when executed by one ormore processors, to cause one or more processors to control a chemicalmechanical system to perform: (a) polishing the substrate with anabrasive-free polishing pad until it is substantially planarized; andthen (b) polishing the substrate with a fixed abrasive polishing pad toremove residual materials disposed thereon.
 20. The computer readablemedium of claim 19, wherein the instructions are arranged for polishingthe substrate with the abrasive-free polishing pad on a rotating,stationary or linear first platen and polishing the substrate with thefixed abrasive polishing pad on a rotating, stationary or linear secondplaten.
 21. The computer readable medium of claim 19, wherein theinstructions are arranged for polishing the substrate at a first removalrate with the abrasive-free first polishing composition to substantiallyremove the bulk copper containing material disposed thereon, providingthe substrate to a second platen containing a fixed abrasive polishingpad, and polishing the substrate at a second removal rate less than thefirst removal rate with a second composition to remove residual coppercontaining materials disposed thereon.
 22. The computer readable mediumof claim 19, wherein the instructions are further arranged for chemicalmechanical polishing the substrate to remove a barrier layer disposed onthe substrate with an abrasive-free third polishing compositionabrasive-free polishing pad mounted on a rotating, stationary or linearthird platen.
 23. The computer readable medium of claim 19, wherein acomputer based control system is used to sequence and control theinstructions for planarizing a substrate surface contained in thecomputer readable medium.